Apparently, they were filming scenes for a new movie by famed director Terrence Malick (Days of Heaven, Badlands, The Tree of Life), which has been shooting at various Austin festivals and concerts since last year. The film doesn't have a title yet (it was previously called Lawless, until another movie with that name came along) and the whole thing is shrouded in mystery.

Here's what we know so far:

The plot:

- Per IMDB: "Two intersecting love triangles. Obsession and betrayal set against the music scene in Austin, Texas."

The actors:

- The film stars Christian Bale, Natalie Portman, Ryan Gosling, Rooney Mara, Cate Blanchett, Michael Fassbender, Holly Hunter, and Skyfall Bond girl Bérénice Marlohe.- Val Kilmer hasn't been confirmed, though his appearance with the Black Lips at Fun Fun Fun would imply as much.- Benicio Del Toro is also rumored to be in the film.

The musicians who may or may not appear in the film:

- The Black Lips, joined on stage by Mara and Kilmer.- Alan Palomo of Neon Indian reportedly shot scenes for the film- Fleet Foxes, who were joined by Christan Bale on bongos at last year's Austin City Limits- Arcade Fire and Iron & Wine, who were also reportedly filmed at last year's Austin City Limits- Die Antwoord, who were on stage at this year's Austin City Limits while Natalie Portman and Michael Fassbender reportedly shot a scene for the film. - Portman was also spotted at Iggy and the Stooges' set at this year's ACL.- YACHT and Big Freedia, who were filmed at last year's Fun Fun Fun Fest.-You can see Gosling and Mara hanging in the background in this "behind the scenes" video for Lykke Li's episode of PBS' "Austin City Limits" TV show.- Patti Smith, who allegedly serenaded Mara during a recent Austin show.- Florence Welch of Florence and the Machine was spotted with Gosling and Mara at this year's ACL.- Tegan and Sara, who played the set immediately following.

- The reports from festivals and live shows probably won't end here. The lead actors are still being spotted around Austin.- Malick may be filming now, but don't expect to see it any time soon. He's a notoriously slow director: the length of time between Days of Heaven and its follow-up, The Thin Red Line, was 20 years.- Malick is also at work on another film called Knight of Cups. Bale, Blanchett, Hunter, and Portman also star in that film, which is about "a man, temptations, celebrity, and excess," according to IMDB. Perhaps it's just a casting coincidence, but there's speculation that the two films are linked somehow.- The non-musical plot point, the one about love triangles? That's pretty much confirmed by the dozens of tabloid reports showing the various actors making out in different Austin locations. Oh look, here's one from Perez Hilton!- One more guest star: resident Austin weirdo Eric "The Lizardman" Sprague.

Here's Kilmer performing with the Black Lips, while Mara plays guitar on the side of the stage: